8.7 Arm Joints

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8.7.1 Status Interface

1. Arm Joint Status

• Description: Obtain the status of both arm joints, including current position, speed, current, and temperature. Applicable to all Walker Tienkung models.

• Communication type: topic

• Topic name: /arm/status

• Message definition: bodyctrl_msgs::msg::MotorStatusMsg

• Message format:

  std_msgs/Header header
  MotorStatus[] status
  
  # MotorStatus definition:
  uint16 name    # MotorName
  float32 pos    # rad
  float32 speed  # rad
  float32 current # A
  float32 temperature
  uint32 error

  error field definition:

  Value	Description
  33072	Device offline
  33073	Joint position out of range
  1	Motor over‑temperature
  2	Over‑current
  3	Under‑voltage
  4	Joint MOS over‑temperature
  5	Stall
  6	Over‑voltage
  7	Phase loss
  8	Encoder error

8.7.2 Control Interfaces

warning

The arm joints can be controlled by custom programs under any of the following two conditions:

1. After stopping the auto-start service (sudo systemctl stop proc_manager.service), manually start only the body service (ros2 launch body_control body.launch.py), and do not start the locomotion control service.

2. Ensure that proc_manager.service is running normally, complete the self-check by pressing A, and then use the remote controller to manually enter upper-body (half-body) control mode (G middle + E middle + F down, then long press A, hear a short beep, then the robot is in half-body control mode. Currently supported only on TienKung Walker Wujiang, and requires software version 2.0.5.2 or above).

1. Position Mode

• Description: Position control interface for arm joints. Requires desired position, desired speed, and maximum current. Applicable to all Walker Tienkung models.

• Communication type: topic

• Topic name: /arm/cmd_pos

• Message definition: bodyctrl_msgs::msg::CmdSetMotorPosition

• Message format:

  std_msgs/Header header
  SetMotorPosition[] cmds
  
  # SetMotorPosition.msg
  uint16 name  # MotorName
  float32 pos  # rad
  float32 spd  # rad/s
  float32 cur  # A

• Example commands:

  ros2 topic pub /arm/cmd_pos bodyctrl_msgs/msg/CmdSetMotorPosition "{cmds: [{name: 12, pos: 0.3, spd: 0.2, cur: 8.0}]}"
  
  ros2 topic pub /arm/cmd_pos bodyctrl_msgs/msg/CmdSetMotorPosition "{cmds: [{name: 22, pos: -0.3, spd: 0.2, cur: 8.0}]}"

2. Hybrid Force‑Position Mode

• Description: Hybrid force‑position control interface for arm joints. Requires desired position, desired speed, feed‑forward torque, and kp/kd gains. Applicable to all Walker Tienkung models.

• Communication type: topic

• Topic name: /arm/cmd_ctrl

• Message definition: bodyctrl_msgs::msg::CmdMotorCtrl

• Message format:

  std_msgs/Header header
  MotorCtrl[] cmds
  
  # MotorCtrl.msg
  uint16 name
  float32 kp
  float32 kd
  float32 pos
  float32 spd
  float32 tor

• Example commands:

  ros2 topic pub /arm/cmd_ctrl bodyctrl_msgs/msg/CmdMotorCtrl "{cmds: [{name: 13, kp: 30.0, kd: 10.0, pos: 0.2, spd: 0.0, tor: 0.0}]}"
  
  ros2 topic pub /arm/cmd_ctrl bodyctrl_msgs/msg/CmdMotorCtrl "{cmds: [{name: 23, kp: 30.0, kd: 10.0, pos: 0.2, spd: 0.0, tor: 0.0}]}"

3. Velocity Mode

• Description: Velocity control interface for arm joints. Requires desired speed and maximum current. Applicable to all Walker Tienkung models.

• Note: Once this message is published, the motor will continue to run at the specified speed until a message with spd = 0.0 is received on the same topic. Use with caution.

• Communication type: topic

• Topic name: /arm/cmd_vel

• Message definition: bodyctrl_msgs::msg::CmdSetMotorSpeed

• Message format:

  std_msgs/Header header
  SetMotorSpeed[] cmds
  
  # SetMotorSpeed.msg
  uint16 name  # MotorName
  float32 spd  # rad/s
  float32 cur  # A

4. Current mode

• Description: The current control interface of the joint requires the supply of the desired current.

• Communication type: topic

• Topic name: /arm/cmd_current

• Message definition: bodyctrl_msgs::msg::CmdSetMotorCurTor

• Message format:

  std_msgs/Header header
  SetMotorCurTor[] cmds
  
  #SetMotorCurTor.msg
  uint16 name # MotorName 
  float32 cur_tor
  uint8 ctrl_status

5. Arm Joint Zeroing

• Description: Zeroing interface for arm joints. When this interface is called, the current position of the specified arm motors is set as the zero position. When the D button on the remote controller is used to return to zero, those joints will move to this position. Typically used together with a dedicated zeroing tool; use with caution if such a tool is not available. Applicable to all Walker Tienkung models.

• Communication type: topic

• Topic name: /arm/cmd_set_zero

• Message definition: std_msgs::msg::String

• Message format:

  Send joint IDs as a string to perform zeroing.
  Arm joint IDs:
    Left arm: 11–17
    Right arm: 21–27